1. Field of the Invention
The present invention relates to an image recording apparatus, an image processing apparatus, an image recording method and an image processing method and a program, and more particularly, to technology for correcting density non-uniformities produced by fluctuation in the properties of respective recording elements when recording an image on a recording medium by using a recording head including a plurality of recording elements.
2. Description of the Related Art
In an image recording apparatus, such as an inkjet recording apparatus including a plurality of nozzles, fluctuation occurs in the ejection characteristics between nozzles due to drying of ink in the nozzle opening sections with the passage of time, and the apparatus comes to include degraded nozzles which have an impediment associated with ink ejection and ejection failure nozzles which cannot eject ink at all. The presence of degraded nozzles or ejection failure nozzles of this kind is not desirable since it leads to permanent disruption of the recorded image, such as white stripes. Therefore, Japanese Patent Application Publication No. 2003-136764 proposes technology for preventing disruption of a recorded image caused by deterioration of the nozzle ejection characteristics.
Japanese Patent Application Publication No. 2003-136764 discloses an inkjet recording apparatus which records an image on a recording medium by ejecting ink from a plurality of nozzles. In this inkjet recording apparatus, patterns for measuring recording characteristics of the recording head (a shading pattern and an ejection failure detection pattern) are output, the density of the patterns is measured and ejection failure nozzles which are in a non-ejecting state are identified on the basis of these measurement results. Furthermore, a density distribution is determined corresponding to each nozzle, and a convolution integral of this density distribution is found using a visual transfer function (VTF) or point spread function (PSF). The results of the portion corresponding to the ejection failure nozzles of the determined density distribution are compared with predetermined reference set values, and on the basis of this comparison result, a complementation table is specified for each nozzle in order to carry out complementation with inks of a different color to the color of the ink to be ejected from the ejection failure nozzle. The image data corresponding to the ejection failure nozzles is converted into ink ejection information of a different color which is ejected from other nozzles, on the basis of the complementation table which is specified in this way.
However, in the technology described in Japanese Patent Application Publication No. 2003-136764, if a new nozzle suffering ejection failure occurs when the shading pattern is output, in other words, if an uncorrected ejection failure nozzle occurs, then the effects of the light scattering produced by the white stripe on the peripheral measurement density are not taken into account. Therefore, there has been a problem in that the density correction of the nozzles peripheral to the uncorrected ejection failure nozzles involves overcorrection. This effect is especially pronounced when using an inexpensive generic scanner having a low resolution.
Furthermore, if density correction is carried out in respect of portions which are liable to be corrected for ejection failure, then correction is duplicated if ejection failure correction has already been carried out, thus resulting in overcorrection.